QI am seeing a lot of magazine ads and posts on the Internet about devices that can solve our energy problems, but it seems to me that these devices would have to generate more energy
than they consume to do what their claims say. What is
your take on this?

Cassie Jefferson
Kissimmee, FL

AThere is some science to help us see why systems that claim to generate more energy than they consume can NEVER be built EVER! Our search begins in the 1800s with French
engineer and physicist, Nicolas Léonard Sadi Carnot who
was trying to perfect the steam engine for use in pumping
water out of mines. Carnot noted that the power output
of the steam engine was proportional to the difference in
temperatures between the boiler and the condenser (which
represents the heat input into the system). Carnot also
noted that part of the heat energy in the system was lost
as it left through the condenser water without being made
to produce useful work (heat is also lost through the walls
of the boiler and piping which cannot be used to generate
useful work).

Wait a minute. What exactly is useful work? Hold on to
your hats! It’s time for a little physics. Energy is defined as
the ability to do work, so let’s look first at energy.

Energy comes in two major forms: (1) Potential Energy
— a stationary energy which is the energy of position in
a force field such as a raised weight or an electron on
a capacitor plate; and ( 2) Kinetic Energy — the energy
of motion such as the energy of a weight falling or an
electron moving through a conductor. Figure 10 shows an
example of mechanical potential and kinetic energies in a
gravitational field using a ball stationary on the top of a hill
or pushed down the hill.

With the ball stationary at the top of the hill, the
potential energy is maximum and the kinetic energy is
zero. As the ball is pushed down the hill, the ball speeds
up continually and its kinetic energy increases until it
reaches a maximum value at the bottom of the hill. In the
meantime, the potential energy decreases until it reaches
its minimum at the bottom of the hill. The good thing
about potential energy is that we can select the reference
plane anywhere in the universe we wish to, but life is easier
if we select a plane somewhere in the area we are studying
(such as the bottom of the hill in this example).

So, now we can define work in terms of expended
energy. Looking at our example of the ball on the hill in
Figure 10, in order to move the ball from the bottom of the
hill as in (a), we had to do work which increased the ball’s
potential energy (PE). When the ball rolled down the hill,
it expended potential energy to increase its kinetic energy

(KE) in (b). Upon reaching the bottom of the hill, the ball
is capable of doing work (W), such as moving an object in
its path.
If there is no energy lost in these two processes, the
maximum kinetic and potential energies are equal; they
also equal the work done to push the ball up the hill and
the work done by the ball at the bottom of the hill. This
is the Principle of the Equivalence of Work and Energy.
The Law of Conservation of Energy (energy cannot be
created or destroyed but can be transmitted, transferred, or
transformed) says in a lossless system (such as our ball on
the hill) the net energy is zero or PEin = KEout = W at any
point along the path of the ball on the hill.
We cannot have a complete discussion of work and
energy without considering the rate at which work is done
or energy is expended. We’ll call this POWER. Power is
simple to calculate by dividing the work or energy by the
time over which the work was done or the energy was
expended:
P = W/t = E/t
where P is the power, W is the work done, E is the energy
expended, and t is the time duration over which the work
was done or the energy was expended. Figure 11 is a good
illustration of power: climbing stairs.
Let’s assume that the “runner” exerts 1,000 Newtons
of force (224.8 pounds to lift and accelerate the runner’s
body weight) to climb the stairs on which the change
in height is 10 meters ( 32 feet - 9. 7 inches). The energy
required or work done in climbing the stairs is 10,000
Newton-Meters (also known as 10,000 joules). If the
“runner” climbs the stairs in 100 seconds, the power is
10,000 joules/100 seconds or 100 joules/second which
we know with the familiar power unit as 100 watts (same
power as a 100 watt incandescent light bulb consumes).

Let’s up the ante and have the runner make the climb
in a blistering 10 seconds. Now the power is 10,000
joules/10 seconds or 1,000 watts. In terms of the electric
n FIGURE 10.
Potential Energy = mgh where m = mass of the ball
(amount of material in the ball), g is the gravitational
constant ( 9.81 meters/second2) and h = height above a
reference plane